It looked like a ring on
the sky. Hundreds of years ago astronomers noticed a nebula with a most unusual
shape. Now known as M57 or NGC 6720, the gas cloud became popularly known as the
Ring Nebula. It is now
known to be a planetary nebula, a gas cloud emitted at the end of a Sun-like star's
existence. As one of the brightest planetary nebula in the sky, the Ring Nebula
can be seen with a small telescope in the constellation of Lyra. The Ring Nebula
lies about 4,000 light years away, and is roughly 500 times the diameter of
our Solar System.[*]